Due, at least in part, to polypropylene's crystallization rate, propylene polymers have been nucleated in a variety of applications, such as injection molding, rotomolding, blown film and solid state stretching processes, for example, with demonstrated improvements in processing and the resulting article's properties. For example, solid state stretched articles formed with nucleated propylene polymers may exhibit increased tenacity, reduced shrinkage and increased transparency.
However, nucleated ethylene polymers have been difficult to stretch with solid state stretching process due, at least in part, to polyethylene's high initial crystal growth rate, which may result in the nucleated ethylene polymer's inability to maintain stretchability. Prior attempts to nucleate polyethylene have therefore been focused on the utilization of specific nucleators in combination with linear low density polyethylene. While success (as measured by increasing crystallization rates) has been achieved with linear low density polyethylene, the ability to nucleate other polyethylenes, such as medium and high density polyethylene have not been demonstrated.
Therefore, a need exists to develop polymers and processes exhibiting improved properties.